1. Field of the Invention
The present invention relates in general to compressors for use in an automotive air conditioning system or the like, and more particularly to compressors of a variable displacement swash plate type.
2. Description of the Prior Art
In FIG. 3, there is diagrammatically shown an air cooling section of a common automotive air conditioning system.
Designated by numeral 1 is a compressor which compresses a refrigerant vapor supplied thereto. The compressed refrigerant vapor from the compressor 1 is supplied to a condenser 2 to be condensed by carrying out a heat exchange with the surrounding air. The condensed or liquefied refrigerant from the condenser 2 is supplied, through a liquid tank 3 and an expansion valve 4, to an evaporator 5 where the refrigerant is subjected to evaporation to cool air which is flowing through the evaporator 5. The cooled air is fed to a passenger cabin of the vehicle. The refrigerant thus heated and vaporized at the evaporator 5 is then supplied to the compressor 1 for repeating the cooling cycle.
As the compressor 1, variable displacement swash plate type compressors are known, which can vary the displacement by changing the inclination angle of a swash plate installed therein.
In order to clarify the task of the present invention, one of the conventional compressors of such type will be described with reference to FIGS. 4 and 5 of the accompanying drawings, which is disclosed in Japanese Patent Second Provisional Publication 64-1668.
As shown in FIG. 4, the conventional compressor 1 comprises a cylindrical casing 6. The casing 6 includes a cylindrical casing proper 7 whose axial open ends are respectively closed by a head case 8 and an end cover 9. Although not shown in the drawing, a plurality of bolts are used for assembling the casing 6.
Within the head case 8, there are defined a low pressure chamber 10 and a high pressure chamber 11. Of course, pressure in the high pressure chamber 11 is higher than that of the low pressure chamber 10. A partition plate 15 is air-tightly interposed between the casing proper 7 and the head case 8. The head case 8 is formed with an inlet port 12a which is communicated with the low pressure chamber 10. The head case 8 is further formed with an outlet port 12b which is communicated with the high pressure chamber 11. The inlet port 12a is connected to an outlet port of the above-mentioned evaporator 5 (see FIG. 3), and the outlet port 12b is connected to an inlet port of the condenser 2 (see FIG. 3).
A drive shaft 13 is coaxially arranged in the casing 6, which passes through the end cover 9. An inner end of the drive shaft 13 is arranged in a center bore 26 defined in the casing proper 7. Two radial needle bearings 22a and 22b and two thrust bearings 23a and 23b are used for permitting smooth rotation of the drive shaft 13 in the casing 6. As shown, the radial needle bearings 22a and 22b directly bear the drive shaft 13 at the center bore 26 and the end cover 9, while, the thrust bearings 23a and 23b indirectly bear the drive shaft 13 at the center bore 26 and the end cover 9. That is, the thrust bearings 23a and 23b are arranged to bear a certain thrust load applied to the drive shaft 13.
The thrust bearing 23a is installed in a stepped portion 25 of the center bore 26 to support an inner end of the drive shaft 13. The thrust bearing 23a is biased leftward in the drawing by an adjusting nut 24 which is meshed with a threaded inner wall of the center bore 26. That is, by turning the adjusting nut 24, an axial force applied to the drive shaft 13 can be adjusted.
The other thrust bearing 23b is interposed between the end cover 9 and an after-mentioned supporting bracket 20.
Within a right half of the casing 6, there are defined a plurality (five or six) of cylinders 14 which are arranged at evenly spaced intervals about an axis of the drive shaft 13. Each cylinder 14 has a piston 16 slidably received therein.
Within a left half of the casing 6, there is defined a crank chamber 18. In the crank chamber 18, a sleeve member 19 having a spherical outer surface 19a is slidably disposed on the drive shaft 13. A supporting bracket 20 is secured to the drive shaft 13 to rotate therewith. As shown, a base part of the supporting bracket 20 is positioned near the end cover 9 to put the thrust bearing 23b therebetween. A coil spring 21 is disposed about the drive shaft 13 to be compressed between the sleeve member 19 and the supporting bracket 20. Thus, the sleeve member 19 is biased rightward, that is, toward the cylinders 14. A stop ring 28 is secured to the drive shaft 13 near the center bore 26 to stop excessive rightward movement of the sleeve member 19. Thus, so long as an after-mentioned swash plate 27 has no external force applied thereto, the sleeve member 19 is forced to take its rightmost position as shown in FIG. 5 wherein the sleeve member 19 abuts against the stop ring 28. In this condition, an inclination angle ".theta." defined by the swash plate 27 and an imaginary plate perpendicular to the axis of the drive shaft 13 is small.
The swash plate 27 is pivotally connected to the spherical sleeve member 19. That is, for this pivotal connection, a center spherical bore 27a formed in the swash plate 27 is slidably disposed on the spherical outer surface 19a of the sleeve member 19. The swash plate 27 is provided at a side facing the supporting bracket 20 with a driven arm 31 which has a guide pin 32 connected thereto.
The supporting bracket 20 is formed with a drive arm 29 which projects toward the swash plate 27. The drive arm 29 has a slanting elongate slot 30 through which the guide pin 32 of the driven arm 31 passes. Due to this arrangement, the swash plate 27 is permitted to pivot within the angular range ".theta." determined by the distance moved by the pin 32 in the slot 30. In accordance with a sliding movement of the sleeve member 19 on and along the drive shaft 13, the swash plate 27 is pivoted about the guide pin 32.
That is, as is shown in FIG. 4, when the sleeve member 19 comes close to the supporting bracket 20 against the force of the coil spring 21, the guide pin 32 comes to the radially outer end of the elongate slot 30 causing the swash plate 27 to pivot about the sleeve member 19 in a direction to increase the inclination angle ".theta.". Under this condition, the stroke of each piston 16 is increased and thus the displacement of the compressor 1 is increased.
While, when the sleeve member 19 moves away from the supporting bracket 20 with an aid of the force of the coil spring 21, the guide pin 32 moves toward the radially inward end of the elongate slot 30 causing the swash plate 27 to pivot in a direction to decrease the inclination angle ".theta.", as shown in FIG. 5. Under this condition, the stroke of each piston 16 is decreased and thus the displacement of the compressor 1 is decreased.
As shown, each piston 16 is provided at a leading end of a stem portion 34 thereof with a shoe holder portion 33. The shoe holder portion 33 holds a pair of shoes 17 and 17 between which a peripheral part of the swash plate 27 is slidably interposed. Each shoe 17 comprises a flat inner surface which slidably contacts the swash plate 27 and a spherical outer surface which is intimately disposed in a spherical recess 35 formed in the shoe holder portion 33. Upon assembly of the two shoes 17 and 17, the two spherical outer surfaces of them constitute a part of an outer surface of a single sphere.
The stem portion 34 of each piston 16 has a guided outer surface which is guided by a guide structure 36 formed on an inner surface of the casing proper 7. That is, due to provision of the guided outer surface and the guide structure 36, an axial movement of the piston 16 is smoothly carried out and an undesired rotary movement of the piston 16 about the axis thereof is suppressed.
In accordance with the pivotal movement of the swash plate 27 under rotation thereof about the axis of the drive shaft 13, the stem portion 34 pushes and pulls the piston 16 into and from the corresponding cylinder 14.
The partition plate 15 is formed with an inlet bore 37 through which the low pressure chamber 10 and each cylinder 14 are communicated. The partition wall 15 is further formed with an outlet bore 38 through which the high pressure chamber 11 and each cylinder 14 are communicated. An inlet valve 39 of reed type is associated with the inlet bore 37 for permitting only inlet flow of a refrigerant vapor into the cylinder 14 from the low pressure chamber 10. An outlet valve 40 of reed type is associated with the outlet bore 38 for permitting only outlet flow of a highly compressed refrigerant vapor into the high pressure chamber 11 from the cylinder 14.
Between the low pressure chamber 10 and the crank chamber 18, there extends a pressure regulating passage 41. Within the passage 41, there is arranged a pressure regulating valve 45. The pressure regulating valve 45 comprises a bellows 42 which effects a telescopic motion in accordance with a surrounding pressure applied thereto and a needle 44 which is fixed to a top of the bellows 42 to close and open an orifice 43 in accordance with the telescopic motion of the bellows 42. The bellows 42 is filled with a gas of predetermined pressure. In accordance with the refrigerant pressure in the low pressure chamber 10, the pressure regulating valve 45 controls the communication between the crank chamber 18 and the low pressure chamber 10 thereby adjusting the pressure in the crank chamber 18.
In the following, operation of the above-mentioned conventional compressor 1 will be described.
When, for operating the cooling section of the automotive air conditioning system, the drive shaft 13 is driven, the swash plate 27 is rotated together with the drive shaft 13 while making "helical turns" about the axis of the shaft 13. Due to the spiral turns of the swash plate 27, each piston 16 is forced to make reciprocating movement in the corresponding cylinder 14, and thus, the refrigerant vapor from the evaporator 5 (see FIG. 3) is sucked into the cylinders 14 through the inlet port 12a, the inlet bores 37 and the inlet valves 39. After being compressed by the pistons 16 in the cylinders 14, the refrigerant vapor is discharged to the high pressure chamber 11 through the outlet bores 38 and the outlet valves 40. The compressed refrigerant vapor in the high pressure chamber 11 is then supplied to the condenser 2 (see FIG. 3).
Under a severe cooling load, it is necessary to compress a larger amount of refrigerant vapor. In this case, the pressure of the refrigerant vapor fed from the evaporator 5 (see FIG. 3) to the low pressure chamber 10 is relatively high, and thus, the pressure in the pressure regulating passage 41 is high. Under this condition, the bellows 42 of the pressure regulating valve 45 is contracted causing the needle 44 to move away from the orifice 43 of the passage 41. As a result, the crank chamber 18 becomes in communication with the low pressure chamber 10 through the orifice 43 and the passage 41, and thus the pressure in the crank chamber 18 is lowered.
During operation of the compressor 1, the pressure in the crank chamber 18 applies to a back face of each piston 16 and the pressure in a compression chamber of the corresponding cylinder 14 applies to a front face of the piston 16. Accordingly, each piston 16 is pressed toward a lower pressure side with a force corresponding to the pressure difference therebetween. Such forces applied to all the pistons 16 are added to determine the inclination angle of the swash plate 27. Of course, the pressure in the compression chamber of each cylinder 14 is subjected to change during the reciprocating movement of the piston 16. However, since such reciprocating movement is carried out at a high speed, it is considered that the pressure in the compression chamber is the average of various degree of pressure continuously produced in the stroke.
When, as is stated hereinabove, the pressure in the crank chamber 18 is lowered and the pressure becomes very low as compared with the pressure in each compression chamber of the cylinder 14, the force for pressing each piston 16 leftward, that is, toward the swash plate 27 is increased. As is mentioned hereinabove, the guide pin 32 for the swash plate 27 is arranged at a radially outer side with respect to the drive shaft 13. Accordingly, the moment applied to the swash plate 27 differs in every piston 16. That is, the moment of pistons 16 positioned close to the guide pin 32 is small and the moment of pistons 16 positioned away from the guide pin 32 is large. Accordingly, when the pressure in the crank chamber 18 is low, the swash plate 27 is largely inclined as shown in FIG. 4. That is, the inclination angle ".theta." is increased. Under this condition, each piston 16 is forced to have a long stroke, and thus, the displacement of the compressor 1 is increased.
Under a lower cooling load, it is only necessary to compress a smaller amount of refrigerant vapor. In this case, the pressure of the refrigerant vapor fed from the evaporator 5 is relatively low, and thus, the pressure regulating passage 41 is low. Under this condition, the bellows 42 is expanded causing the needle 44 to move into the orifice 43 to close the same. As a result, the crank chamber 18 becomes isolated from the low pressure chamber 10. In this state, the pressure in the crank chamber 18 is gradually increased due to penetration of high pressure refrigerant vapor (or blowby gas) thereinto through a clearance between each piston 16 of the cylinder 14.
When, as is stated hereinabove, the pressure in the crank chamber 18 is increased and the pressure becomes higher than that in each compression chamber of the cylinder 14, the force for pressing each piston 16 leftward, that is, toward the swash plate 27 is lowered. Accordingly, the swash plate 27 is moved rightward due to the force of the coil spring 21 and inclined slightly as shown in FIG. 5. That is, the inclination angle ".theta." is decreased. Under this condition, each piston 16 is forced to have a short stroke, and thus, the displacement of the compressor 1 is lowered.
Under a medium cooling load, the pressure regulating valve 45 regulates the pressure in the crank chamber 18 at a medium level. In this case, the swash plate 27 shows a posture between the posture of FIG. 4 and that of FIG. 5.
However, due to inherent construction, the above-mentioned conventional compressor 1 has the following drawbacks.
(1) Machining both the guide structure 36 on the inner surface of the casing proper 7 and the guided outer surface on each piston 16 needs a very troublesome and expensive technique, which thus increases the production cost of the compressor 1.
(2) Due to presence of a clearance inevitably defined between the guide structure 36 and the guided outer surface, a slight but assured pivoting of each piston 16 about its axis is produced under operation of the compressor 1. However, this pivoting tends to cause a collision of the guided outer surface against the guide structure 36, which produced a marked noise.